Paper triangles help to distinguish bacteria

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Published: Jul 28, 2014

Author: Steve Down

Channels: Chemometrics & Informatics / Base Peak

The recently developed paper spray mass spectrometry can distinguish between bacteria at the species level within a couple of minutes. This latest application of the ambient ionisation technique has been described in Analytical Chemistry where it was used to discriminate between 16 Gram-positive and Gram-negative bacteria.

For paper spray, a small amount of sample, in this case material from the bacterial cultures, is smeared on to a small paper triangle followed by a spot of solvent. When a voltage is applied to the paper, charged droplets of the sample are released from a point on the triangle and drawn into the mass spectrometer.

The principal ions from bacteria were phospholipids, phosphatidylethanolamines dominating in positive-ion mode and phosphatidylglycerols in negative-ion mode. Rather than relying on visual discrimination, principal components analysis with linear discriminant analysis was employed to facilitate classification.

In this way, the selected Gram-positive species were discriminated with a 98% success rate and the Gram-negative species with 87% success. When two closely related bacteria were mixed, discrimination was successful when the positive- and negative-ion spectra were considered together.

The researchers, who included Graham Cooks from Purdue University who developed desorption ionisation mass spectrometry 10 years ago, described the new approach as "as a promising strategy to identify bacteria, provided that a sufficiently large database can be created. The data in this paper establish a foundation for the expansion of the experiment to the development of a large library of microorganisms including a wide variety of species, strains, and culture media."